Organo-metallic tin catalysts for preparation of polyesters



United States Patent ORGANO-METALLIC TIN CATALYSTS FGR PREPARATION OFPOLYESTERS John R. Caldwell, Kingsport, Term., assignor to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey No Drawing.Application October 3, 1952, Serial No. 313,078

13 Claims. (Cl. 260-75) This invention relates to a process forpreparing polyesters which comprises condensing a diester of adicarboxylic acid with a polyhydroxy compound in the presence of atleast one of a group of novel catalytic condensing agents which areorganic derivatives of tin and which are defined below. These novelcatalytic condensing agents can be advantageously employed in thepreparation of linear polyesters wherein the dicarboxylic acid is anaromatic compound which does not contain any ethylenic (olefinic)unsaturation and the polyhydroxy compound is a dihydroxy compound. Inpreparing such linear polyesters it is advantageous to conduct thecondensation in an inert atmosphere at an elevated temperature which isincreased during the course of the condensation up to a temperature offrom about 225 to about 310 C., the condensation being conducted duringthe latter stages thereof at a very low subatmospheric pressure.

This application contains subject matter disclosed to some extent in acopending application, Serial No. 143,594, filed February 10, 1950, byJ. R. Caldwell, now U. S. Patent No. 2,614,120, dated October 14, 1952.This application also contains subject matter disclosed in othercopending applications filed on even date herewith by J. R. Caldwell,Serial Nos. 313,061 through 313,071.

Various polyesters of dicarboxylic acids and polyhydroxy compounds arewell known in the prior art and have been used, for example, in themanufacture of paints and varnishes. Moreover, prior art disclosures setforth various linear condensation polyesters derived from dihydroxycompounds and dibasic acids such as terephthalic acid which are capableof being drawn into fibers showing by characteristic X-ray patterns,orientation along the fiber axis. However, many of these linearpolyesters possess a relatively low melting point and a fairlyconsiderable solubility in various solvents whereby they are ofrestricted utility, especially in the textile field. These polyestersvary considerably in their characteristics, depending on the particulardicarboxylic acid and the particular polyhydroxy compound employed.Generally speaking, these polyesters have various physicalcharacteristics which are not as satisfactory as could be desired,

The preparation of polyesters is well known in the prior art andinvolves the reaction of a dibasic dicarboxylic acid with a dihydric orpolyhydric alcohol. It is advantageous to employ estersof thedicarboxylic acid whereby ester interchange takes place with the glycolor polyhydric alcohol to form a polyester and an alcohol; When using theester interchange method, the time required to form the polyesters isgenerally considerably less than when thefree dicarboxylic acid isemployed. The long chain in the polyester is built up by a series ofester interchange reactions wherein the glycol displaces a relativelylow-boiling alcohol component of the acid ester to form a glycol ester.During the last stages of the reaction, it is generally desirable toheat the condensing reaction mixture to a temperature of about 225 -275C. or higher in order tomaintain the fluid state; For this reason, the

ICC

2 properties of the catalytic condensing agent are very important.

A desirable catalytic condensing agent must be active enough to promoteester interchange at a temperature below the boiling point of the glycolor other polyhydric alcohol. At the same time, the catalyst must bestable at temperatures of 225 -3 10 or even higher if necessary.Furthermore, the catalyst must not cause decomposition or degradation ofthe polyester at these high temperatures.

In accordance with this invention, it has been found that certaincompounds are especially valuable for use as catalytic condensing agentsin the preparation of high melting linear polyesters. These catalystsare tin compounds containing at least one organic radical. Thesecatalysts include compounds of both divalent or tetravalent tin whichhave the general formulas: set forth below:

aa-eas eas aa e-a wherein M is an alkali metal, e. g. lithium, sodium,or potassium, M is an alkaline earth metal such as Mg, Ca or Sr, each Rrepresents analkyl radical containing from 1 to 8 carbon atoms, each Rradical represents a substituent selected from those consisting of alkylradicals containing from 1 to 8 carbon atoms (i. e. R radicals) and arylradicals of the benzene series containing from 6 to 9 carbon atoms (e.g. phenyl, tolyl, benzyl, phenylethyl, etc., radicals), and Acrepresents an acyl radical derivedfrom an organic acid containing from 2to 18 carbon atoms (e. g. acetyl, butyryl, lauroyl, benzoyl, stearoyl,etc.).

These novel catalysts can. be advantageously employed in processes forpreparing polyesters, which processes are described below. These novelcatalysts are effective only when substantially anhydrous conditions areemployed and no free acid is present to a sufficiently significantextent to destroy the catalyst compound; thus, when free acids areemployed the acids are first reacted with a hydroxy compound (preferablythe polyhydroxy compound to be employed in the polyesterificationprocess) before the novel catalyst of this invention is added.

The novel bimetallic alkoxide catalysts can be made as described byMeerwein, Ann. 476, 113 (1929). As shown by Meerwein, these catalystsare not merely mixtures of the two metallic alkoxides. They are definitecompounds having a salt-like structure. These are the compounds depictedabove by the Formulas A through H. Those not specifically described byMeerwein can be prepared by procedures analogous to the working examplesand methods set forth by Meerwein.

The other tin compounds can also be made by various methods such asthose described in the following literature:

For the preparation of diaryl tin dihalides (Formula P) see Ber. 62, 996(1929); J. Am. Chem. Soc. 49, 1369 (1927). For the preparation ofdialkyl tin dihalides (Formula P) see I. Am. Chem. Soc. 47, 2568 (1925);C. A. 41, 90 (1947). For the preparation of diaryl tin oxides (FormulaM) see I. Am. Chem. Soc. 48, 1054 (1926). For the preparation oftetraaryl tin compounds (FormulaK) see C. A. 32, 5387 (1938). For thepreparation of tin alkoxides (Formula J) see C. A. 24, 586 (1930). Forthe preparation of alkyl tin salts (Formula Q) see C. A. 31, 4290. Forthe preparation of alkyl tin compounds (Formula K and L) see C. A. 35,2470 (1941); C. A. 33, 5357 (1939). For the preparation of alkyl aryltin (Formulas K and L) see C. A. 31, 4290 (1937); C. A. 38, 331 (1944).For the preparation of other tin compounds not covered by thesecitations see Die Chemie der Metal-Organishen Verbindungen, by Krauseand V. Grosse, published in Berlin, 1937, by Gebroder- Borntrager.

The tin alkoxides (Formulas I and I) and the bimetallic alkoxides(Formulas A through H) contain R substituents which can represent bothstraight chain and branched chain alkyl radicals, e g. diethoxide,tetramethoxide, tetrabutoxide, tetra-tert-butoxide, tetrahexoxide, etc.

The alkyl derivatives (Formulas K and L) contain one or more alkylradicals attached to a tin atom through-a direct C-Sn linkage, e. g.dibutyl tin, dihexyl tin, tetrabutyl tin, tetraethyl tin, tetramethyltin, diocyl tin, etc. Two of the tetra-alkyl radicals can be replacedwith an oxygen atom to form compounds having Formula M, e. g. dimethyltin oxide, dimethyl tin oxide, dibutyl tin oxide, diheptyl tin oxide,etc.

Complexes can be formed by reacting dialkyl tin oxides with alkali metalalkoxides in an alcohol solution to form compounds having Formula N,which compounds are especially useful catalysts, e. g. react dibutyl tinoxide with sodium ethoxide, etc. The actual structure of compoundsdepicted by Formula N has not been definitely established. This formulais intended to represent the reaction products described. Tin compoundscontaining alkyl and alkoxy radicals are also useful catalysts (seeFormula e. g. diethyl tin diethoxide, dibutyl tin dibutoxide, dihexyltin dimethoxide, etc.

Salts derived from dialkyl tin oxides reacted with carboxylic acids orhydrochloric acid are also of particular value as catalysts, seeFormulas P and Q. Examples of these catalytic condensing agents includedibutyl tin diacetate, diethyl tin dibutyrate, dibutyl tin dilauroate,dimethyl tin dibenzoate, dibutyl tin dichloride, diethyl tin dichloride,dioctyl tin dichloride, dihexyl tin distearate, etc.

' The tin compounds having Formulas K, L and M can be prepared whereinone or more of the R radicals represents an aryl radical of the benzeneseries, e. g. phenyl, tolyl, benzyl, etc. Examples include diphenyl tin,tetraphenyl tin, diphenyl dibutyl tin, ditolyl diethyl tin, di-

phenyl tin oxide, dibenzyl tin, tetrabenzyl tin, di(fi-phenylethyl) tinoxide, dibenzyl tin oxide, etc.

The novel catalysts of this invention give a very rapid reaction rate atall stages of the polyesterification process, including the final stepwhere the molecular weight is built up. They are particularly valuablefor the preparation of high melting polyesters from 1,6 hexanediol and1,5-pentanediol. It is well known that these glycols have a tendency todecompose at temperatures above 250260 C. and hence are difficult touse. With the novel catalysts described above polyester reactionsemploying these glycols can be carried out at temperatures up to 300 C.or even higher without excessive decomposition.

The novel catalysts can, in general, be employed for the preparation ofsubstantially all polyesters involving an ester interchange reactionbetween a dicarboxylic acid ester and a glycol or glycol ester. Thecatalysts are especially valuable for the preparation of polyesters thatmelt above about 240 C., as for example, polyethylene terephthalate. Theprocess of the invention is applicable to all of the polyestersdescribed herein.

By employing the novel catalysts of this invention, the reaction rate ofthe polyesterification process can be increased by a factor which isgenerally from about 2 to 5 times the reaction rate obtainable whencatalysts known in the prior art are employed. The tin compounds of thisinvention give reaction rates that are 5 to 10 times faster than thereaction rates when metallic tin is used as alluded to in the prior art.Moreover, the novel catalysts of this invention have the valuablecharacteristic of minimizing side reactions which have the tendency ofcausing considerable degradation of the polyester products at therelatively high temperatures employed in preparing highly polymericpolyesters. Furthermore, by employing these novel catalysts to increasethe rate of condensation, the time available for possible decompositionof the high molecular weight polyester molecules being formed at hightemperatures is appreciably reduced. Thus, by increasing the reactionrate, the time required to make a polyester is reduced which is quiteimportant because at 250-300 C. the degree of color formation and extentof deleterious side reactions is proportional to the time of heating.

The polyesters produced when employing these novel catalysts havegreatly improved properties as compared to products obtained employingcatalysts known in the prior art. The molecular weight is considerablyhigher whereby highly polymeric polyesters are obtained. The color ofthe polyesters obtained is excellent; the products can therefore beemployed for purposes calling for white or colorless materials. Thephysical properties of the polyesters obtained are also superior. Athigh tempera tures there is a great improvement in the inherentviscosities of linear polyesters which are suitable formelt spinning orextrusion whereby fibers, films, etc., can be produced having propertiessuperior to those obtainable With known catalysts.

The herein described novel catalysts are especially valuable for thepreparation of polyesters employing diesters of p,p'-sulfonyl dibenzoicacid as described in copending applications filed on even date herewithby I. R. Caldwell, Serial Nos. 313,061 through 313,068. Many of thesepolyesters are very high melting and the reaction must often be carriedout at a temperature of 280-300 C. or higher. It has been found thatrelatively few catalysts are effective at this temperature other thanthose described in this application.

It is an object of this invention to provide new and improved catalyticcondensing agents for promoting the formation of improved polyesters inprocesses involving ester interchange and alcoholysis. A further objectof this invention is to provide a new and improved method for thepreparation of polyesters wherein such new and improved catalysts areemployed. Other objects will become apparent elsewhere in thisspecification.

A broad aspect of this invention relates to a process for preparing apolyester which comprises condensing under substantially anhydrousconditions at an elevated temperature in aninert atmosphere a diester ofa dicarboxylic acid with from about 1 to about 10 equivalent proportionsof a polyhydroxy compound, in the presence of a tin compound containingat least one organic radical as a catalytic condensing agent, especiallythose compounds of tin whose formulas have been depicted above.

More specifically, this invention relates to a process sweeper forpreparing a polyester comprising (A) condensing under substantiallyanhydrous conditions an aromatic dicarboxylic acid diester having theformula:

wherein. R1 and R4 each represents a substituent selected from the groupconsisting of an alkyl radical containing from 1 to carbon atoms and anomega-hydroxyalkyl radical containing from 2 to 12 carbon atoms, R2 andR3 each represents (CHzM-r wherein n isa positive integer of from 1 to 5inclusive and X represents a divalent aromatic radical selected from thegroup having the followingxformulas:

and

whereinY represents a divalent radical selected from the groupconsisting of and t mes-1 cm wherein m is a positive integer of from 1to 5 inclusive, (B) with an alpha, omega-dioxy compound selected fromthe group consisting of those compounds having the following formulas:

wherein p represents a positive integer of from2 to 12 inclusive,RsandRs each represents a substituent selected from .the groupconsisting of a hydrogen atom and anacyl radical containing from: 2. to4carbon atoms, R7 representsan alkylene radical containingfrom 2 to 4carbon atoms andq represents a positive integer of from 1 to 10inclusive, the alpha; omega-dioxy compound being. employed in such aproportion that there is at least an equivalent amount of alpha:andomega oxy substituents inproportion. to the carbalkoxy substituentsin the overall combination of the aromatic diesters and the alpha,omega-dioxy compounds, (C). in the presence of a condensing agentselected from the group consisting of the novel catalysts set forthabove, (D) at an elevated temperature which is increased graduallyduring the course of the condensation up to a temperature of from about225 to. about 310 C., (E) the condensation being conducted in aninertatmosphere, (F) and conducting the condensation at atvery low pressureof the inert atmosphere during'thelatter part of the condensation.

, Advantageously, the condensing agent is employed in an. amount offromnabout 0.005% to about 0.2% based on. the. weight of the aromaticdicarboxylic acid diester. Higher and lower proportions can alsobe-employed.

Advantageously, the alpha, omega-di oxy compound is employed in suchaproportion that there are from about 1.2 to about 3 alpha and omegaoxysubstitutents in proportionto the. carbalkorry substituents in theoverall combination of the aromatic diesters and the alpha, omegadioxycompounds. Higher (e. g. 10) and lower (eg. 1) proportions can also'beemployed.

Since the alpha, omega-dioxy compounds which can be employed inaccordance with this invention are most advantageously alpha,omegaadihydroxy compounds and in: order to facilitate the phraseologywhich is employed in. this specification, such compounds willhereinafter be referred to as polyhydroxy or dihydrox y compoundsalthough it is to be understood that the alpha, omega-dioxy compoundsofthe type described above are intended tobe covered by the termdihydroxy compounds or the. term polyhydroxy compounds as such terms areemployed herein- Advantageously, the temperature employed during theearlier part of the condensation is from about to about 220 C. Higherand lower temperatures can also be employed.

Advantageously, the low pressure definedunder (F) is less than about 15mm. of Hg pressure (preferably less than 5' mm.). However, somewhathigher pressures can also be employed.

Most advantageously, the aromatic dicarboxylic acid diester is a diesterof p,p'-sulfonyl dibenzoic acid or terephthalic acid and the polyhydroxycompound is a poly methylene glycol.

This invention also includes processes as described above wherebypolyesters can be prepared by replacing a part of the described aromaticdib'asic acid diester with an ester of a replacement acid which can bean aliphatic dibasic acid, e. g. carbonic acid, oxalic acid, succinicacid, adipic acid, sebacic acid, ot-,a-dimethylglutaric acid,dirnethylrnalonic acid, diglycollic acid, B-oxydipropionic acid,y-oxydibutyric acid, maleic acid, fumaric acid, itaconic acid, etc.Similarly, other esterified acidic moditiers can also be incorporated inconjunction with or in.

lieu of these replacement acid esters, e. g. linoleic. acid, linolenicacid, fatty acids of linseed oil, soybean oil, cottonseedoil, tung oil,etc. Thesenovel'tin catalysts are of great value in the preparation ofpolyesters containing adipicacid. In generahthe catalysts describedintheprior art givendeeply colored; polyesters when adipic' acid is usedattemperatures higher than 230 C. The tin catalysts described hereingive high molecular weight, substantially. colorless polyesters withadipic acid at temperatures as high as 280 C.

The process described above for the general practice of this inventionneed not. be appreciably modified when various partial replacement acidesters are employed in conjunction with the aromatic dibasic acid estersexcept when they are unsaturated and tend to form insoluble andinfusible products due to cross-linkage effects, in which event theprocess described hereinabove is: advantageously terminated at anintermediate temperature of about 250 C. before the pressure is reducedwhereby products are obtained which can be called soluble intermediatepolyesters which are useful in. preparing protective coatings. Thevarious polyesters containing replacement acid esters as describedinthis paragraph can be prepared according to procedures similar to thosedescribed in copending applications filed on even date herewith by J. R.Caldwell, Serial Nos. 313,062 through 313,066.

Polyesterscan alsobe prepared in accordance withthis invention byreplacing a part of the described dihydroxy compound with what can becalled a p'olyhydroxy compound which contains 3 or more hydroXyradicals, e. g. glycerol, sorbitol, pentaerythritol, dipentaerythritol,fimethylglycerol, Z-methyI-Z-hydroxymethyl 1,3- propanediol,1,2,4-trihydroxybutane, etc. In the preparation of polyesters employingthese polyhydroxy compounds, the reaction mixture is not generallyheated to the high temperatures under reduced pressure asdescribedhereihabove since the porduct would become insoluble and infusible dueto cross-linking of the molecules; hence, the process is halted at about250 C. or less prior to the reduction in pressure'of the inertatmosphere. Various solutions can then be prepared from these solublepolyester products which can then be cast into films or otherwise usedin pro tective coating compositions. In preparing such solublepolyesters it is generally advantageous to employ an unsaturatedaliphatic dibasic acid diester in lieu of a part of the describedaromatic dibasic acid diesters, e. g. maleic, fumaric and itaconicdiesters. The various polyesters containing replacement polyhydroxycompounds as described in this paragraph can be prepared according toprocedures similar to those described in a copending application filedon even date herewith by J. R. Caldwell, Serial No. 313,069.

The dihydroxy or polyhydroxy compounds defined above may not actuallycontain any free hydroxy radicals since they may be in esterified formas indicated by the formulas of the dihydroxy compounds set forth above.However, these hydroxy or substituted hydroxy radicals are referred togenerally as hydroxy or substituted hydroxy radicals are referred togenerally as hydroxy radicals or substituents. Each diester isconsidered as containing two carbalkoxy radicals as that term isemployed in the definition of the process as described above since R1and R4 may be alkyl radicals, or omega-hydroxylalkyl radicals. Even whenthe process is preceded by the preliminary step described belowemploying free acids, the term carbalkoxy radicals in the description ofthe process is intended to encompass such free carboxy radicals.

Furthermore, this invention covers processes as defined above whereinthe aromatic dicarboxylic acid diester is formed by a preliminary stepcomprising condensing an aromatic dicarboxylic acid having the formula:

HOOC-R2XR3COOH (wherein R2, R3 and X are defined under (A) in theabovedescribed process), with a polyhydroxy compound which is definedabove under (B) and is employed in the proportions set forth under (B),at an elevated temperature, after which preliminary step the novelcatalytic condensing agent which is defined under (C) is added and thecondensation is completed as defined under (D), (E) and (F).Advantageously, the elevated temperature employed during the preliminarystep is substantially that at which reflux conditions subsist; however,higher and lower temperatures can also be used. Advantageously, asindicated hereinbefore, the polyhydroxy compound is employed in such aproportion that there are from about 1.2 to about 3 hydroxy substituentsin proportion to the acid substituents in the overall combination of thearomatic diester and the polyhydroxy compound.

In preparing polyesters, especially linear highly polymeric polyesters,it is important to exclude oxygen and moisture at all stages of thecondensation, particularly during the latter stages thereof. An inertatmosphere is employed to exclude oxygen; such atmospheres includehelium, hydrogen, nitrogen etc. The reacting materials employed in thecondensation are advantageously substantially anhydrous; however, ifwater is initially present or is formed during the course of thecondensation, it can be-substantially completely removed prior to thefinal stages of the condensation by operating in accordance with thespecified process or otherwise.

Examples of aromatic dicarboxylic acid diesters which can be employed asdefined above under (A) include the ,B-hydroxyethyl diester ofp,p-sulfonyl dibenzoic acid, p,p-sulfonyl dibenzoic acid dibutyl ester,m,p-sulfonyl dibenzoic acid dipropyl ester, m,m-sulfonyl dibenzoic aciddihexyl ester, methyl terephthalate, hexyl terephthalate,- isopropylterephthalate, as well as various esters having the following formulas:

C O-O C3111 CaHwO-O CGCHrO-OH Gamer CO-OCH:

CO-OC H11 CaH10-O C-OOGOQC o-o 03111 et cetera.

The dihydroxy compounds which can be employed to form highly polymericlinear polyesters are straight-chain alkane diols, viz. polymethyleneglycols, wherein the hydroxy radicals are positioned at the two ends ofthe alkylene chain. Examples of such glycols include ethylene glycol,1,3-propylene glycol, 1,4-butylene glycol, 1-6- hexylene glycol,1,10-decamethylene glycol, 1,12-dodecamethylene glycol, etc. Asindicated above, mono or diesters of these glycols can also be employed.Thus, the acetates, propionates and butyrates arerexamples of suchesters. The defined ether glycols can be employed either in lieu of thepolymethylene glycols or in conjunction therewith as modifiers. Examplesof ether glycols include diethylene glycol, triethylene glycol,tetraethylene glycol, bis (4-hydroxybutyl) ether, bis (3-hydroxypropyl)ether,

etc.

Valuable fibers can be advantageously prepared employing the highermelting polyesters which can be produced according to the proceduresdescribed herein.

Preferably no aliphatic ether glycol is employed when fibers are to beprepared. Furthermore, the aromatic acid diesters should ordinarilycontain only p,p linkages when highly polymeric linear polyesters aredesired. However, on the other hand, valuable polyesters can be preparedemploying aliphatic ether glycols without any polymethylene glycolalthough the product obtained will not be suit able for forming usefulfibers. The same applies to the employment of aromatic diesterscontaining linkages in other than the para positions.

The catalytic condensing agents which can be employed have beendescribed above. From about 0005 to about 0.2% of such catalysts basedon the weight of the diesters being condensed can be employed. Higher orlower percentages can also be employed. Generally, from about 0.01% toabout 0.06% of the catalytic condensing agent can be advantageouslyemployed based on the weight of the various diesters being condensed.

The temperature at which polyesterification can be conducted isdependent upon the specific reactants involved in any given reaction. Ingeneral, the reaction mixture can be heated with agitation at from about150 to about 220 C. for from approximately one to three hours in aninert atmosphere (e: g. nitrogen or hydrogen); the mixture can then beheated with agitation atfromabout 225- 240 to about 280-310 C. in thesame atmosphere for approximately 1 to 2 hours. Finally, the pressurecan be greatly reduced to form. a vacuum (less than about 15 mm. of Hgpressure) while the temperature is maintained in the same range (225-3106.); these conditions are advantageously maintained for approximately 1to 6 additional hours. This. final phase is advantageously carried outwith good agitation under the high vacuum in order to facilitate theescape of volatile products from the highly viscous melt. The conditionscan be varied considerably depending upon the degree ofpolyesterification desired, the ultimate properties sought, thestability of the polyester being produced; and the use for which theproduct isi'ntend'ed:

The reaction can be carriedout in the presenceor absence of a solvent.Inert, high boiling compounds, such as diphenyl ether, diphenyl, mixedtolyl sulfones, clorinated naphthalene, chlorinated diphenyl, dimethylsulfolane, etc., can beusedas the reactionmedium.

In the examples given below, the hot bar sticking temperature isreferredto' in several instances. The hot bar sticking testcan bebriefly described as follows: A polyesterfiber is placed on the flatsurface of a heated bar and a weight of 100 grams is applied to thefiber along a distance of inch of the fiber length. The contactsurfaceof this weight has a coating of polytetrafliloroethyl ene whichacts as a thermal insulator. The fiber is allowed to remain-incontactwith the bar under this weight for one minute; The minimum temperatureat which the fiber adheres to the hot barunder these conditions is thesticking'temperature'as that term is employed in the examplesgivenherein:

This invention can be further illustrated by the followexamples; inaddition to these examples it.is apparent that other variations andmodifications thereof can be adapted to obtain similar results:

Example ].Dibutyl tin diacetate as the catalyst One hundred grams p,p-sulfonyldibenzoic acid butyl ester and 45 g. 1,5-pentanediol wereplaced in a reaction vessel equipped with a stirrer, a shortdistillation column and an inlet tube for purified nitrogen. One-tenthgram of dibutyl tin diacetate Was added and the mixture stirred at200-210" C. in an atmosphere of purified nitrogen. After one hour, thedistillation of butyl alcohol ceased, and the temperature wastraisedto275280 C. where it was held for 20 minutes. A vacuum of 0.5 to 1.0 mm.of Hg pressure was applied for 40-60 minutes while the temperature wasmaintained at 275-280 C. A colorless product having an inherentviscosity of 0.80-0.90 in 60 phenol-40 tetrachlorethane solution wasobtained. Fibers pulled from the melt and cold drawn 400-500% show asticking temperature of 240-250 C. The product is also useful for filmsand sheets.

Example 2.--Diphenyl butyl tin as the catalyst 0.05 g. of diphenyldibutyl tin in place of dibutyl tin diacetate was employed in the sameprocess using the same apparatus as in Example 1. A product was obtainedhaving an inherent viscosity of' 0.70-0.80.

110 Example 3.-Dibutyl tin oxide. as the catalyst.

0.06 g. of dibutyl tin oxide in place of dibutyl tin diacetate wasemployed in the same process using'the same apparatus as in Example 1. Aproduct was obtained which was essentially the same. as in Example 1.;

Example 4.-Dibutyl tin dichloride as the catalyst One hundredgrams.p,p-sulfonyl dibenzoic acid ethyl ester and 50 g. of1,6-hexanediol were placed in a vessel equippedwith a variable speedstirrer of the anchor type, a short distillation column, and a gas inlettube for purified hydrogen. Dibutyl tin dichloride (0.08 g.)" was addedand: the mixture heated at 200-210" for I to 1 /2 hours, in anatmosphere of purified hydrogen. During. this time, the distillation ofethyl alcohol from the reaction mixture took place. The temperature wasthen raised to 270- 280 C. and held for 15 minutes. The hydrogen gas wasthen shut off and a vacuum of about 1 mm. of Hg was applied. Themeltrapidly' increased in viscosity andthe reaction was stopped in 30-40minutes. The melt was clear and. colorless. After cooling slowly, theproduct obtained is hard and opaque, due to erystallinity. If the meltis suddenly cooled or quenched, it has a. tendency to remain amorphousand transparent. On a microscope hot stage in polarized light, thecrystalline material shows a melting point of 270280 C. The inherentviscosity in 60% phenol-40% tetrachlorethane is 0.70-0.80. Fibers can bepulled from the melt and cold drawn 500600%. They stick to the hot barat 230-240 C. The polyester can be used to form valuable sheetsandfilms.

Example 5.Dibutyl tin dibutoxide as the catalyst Example 6.Diphenyldibeitzyl tin as the catalyst Diphenyl dibenzyl tin (0.02 g.) wasemployed in the same process using the same apparatus as in Example 5. Aproduct was obtainedwhich was essentially the same as in Example 5.

Example 7.-Dibtltyl tin dilaumte as the catalyst Four hundred and twentygrams (1.0 mole) of p,p'- sulfonyldibenzoic acid butyl ester, 58g. (0.33mole) of dimethyl adipate, and 250 g; 1,5-pentanediol were placed in areaction vessel as described in Example 1. Threetenths of a gram of?dibutyl tin dilaurate was added, and the-'mixture heated'and stirredaccording to the schedule given in Example 1, except that a finaltemperaure of 260 was employed. The product obtained has an inherentviscosity of 0.82m 60% phenol-40% tetrachlorethane.

Example 8.-Dz'buzyl tin diacetate as the catalyst 0.2 gram moleof'p,p'-dicarboxybiphenyl diethyl ester was used in place of the g. ofthe p,p.'-sulfonyldibenzoic acid butyl ester employed in Example 1according tbrthesame process in thesame apparatus as in Example 1..Th'eproducttobtained was similarttothat described in Example: 1:. but.lowen melting.

Example 9.-Dibutyl tir'tdiacetate as the catalyst 0.2. gram. mole ofp,p-dicarboxydiphenylmethane. dibutyl ester wasusedain'place'of thep,p--sulfonyldihenzoic acid butyl estep in: Example 1 according to thesame process" employing. the. same apparatus as in Example 1.The'polyester was similar to'that obtained in Example I butrlower.melting.

Example 10.Dihatyl tin dichloride as the catalyst 100 g. ofp,p'-dicarboxydiphenylether diethyl ester was used in place of thep,p-sulfonyldibenzoic acid ethyl ester in Example 4 according to thesame process employing the same apparatus as in Example 4. The polyesterobtained was similar to that of Example 4 but is lower melt- Example11.-Dibutyl tin dichloride as the catalyst One hundred grams of1,2-di(p-carboxyphenoxy)ethane diethyl ester and 50 g. ethylene glycolwere condensed as described in Example 4 using the same process andapparatus as described in that example. The product was a polyesterhaving a lower melting point than in Example 4.

.Example 12. -Dibutyl tin dihcloride as the catalyst One hundred gramsof p,p-dicarboxydiphenylsulfide dimethyl ester and 50 g. 1,4-butanediolwere condensed as described in Example 4 according to the processdisclosed therein using the same apparatus. The polyester productobtained was similar to that described in Example 4 but it has a lowermelting point, lower viscosity and is generally not as valuable althoughuseful films, sheets, etc. can be prepared therefrom.

Example 13.Dibutyl tin dibatoxide as the catalyst One gram mole ofp,p-dicarbethoxydiphenyl methane and 2.1 gram moles of ethylene glycolwere condensed in apparatus as described in Example 5 according to theprocedure set forth therein employing 0.02 gram of the same catalyst.The product obtained was a highly polymeric linear polyester useful as amolding resin, for preparing films, sheets, etc.

Example 14.-Dibatyl tin dibutoxide as the catalyst One gram mole ofp,p-dicarbomethoxybenzophenone and 2.4 gram moles of trimethylene glycolwere condensed in apparatus as described in Example 5 according to theprocedure set forth therein employing 0.02 gram of the same catalyst.The product obtained was a highly polymeric linear polyester useful as amolding resin, for preparing films, sheets, etc.

Example 15.Dibatyl tin dibatoxia'e as the catalyst One gram mole of1,2-bis(p-carbopropoxyphenoxy) ethane and 2.5 gram moles oftetramethylene glycol were condensed in apparatus as described inExample 5 according to the procedure set forth therein employing 0.02gram of the same catalyst. The product obtained was a highly polymericlinear polyester useful as a molding resin, for preparing films, sheets,etc.

Polyesters similar to those described in the above examples can beprepared employing l,4-bis(p-carbamyloxyphenoxy) benzene, bis(p-carbethoxybenzyl)sulfide and N,N bis(p-carbohexoxyphenyl)methylamine, condensed with ethylene glycol,tetramethylene glycol and hexamethylene glycol.

In the various formulas given for the catalysts in the above examples,C4H9 and the formulas for other such alkyl radicals are intended torepresent the straight chain alkyl radicals. However, branched chainradicals can also be employed.

I claim:

1. A process for preparing a polyester comprising (A) condensing undersubstantially anhydrous conditions an aromatic dicarboxylic acid diesterhaving the formula:

wherein R1 and R4 each represents a substituent selected from the groupconsisting of an alkyl radical containing from 1 to carbon atoms and anomega-hydroxyalkyl radical containing from 2 to 12 carbon atoms, R2 andRs each represents (CHz)n1 wherein n is a positive integer of from 1 to5 inclusive, and X represents a divalent aromatic radical selected fromthe group consisting of those having the following formulas:

and

wherein Y represents a divalent radical selected from the groupconsisting of ((IJH2) mi-C Ha .N

wherein m is a positive integer of from 1 to 5 inclusive, (B) with analpha, omega-dioxy compound comprising a compound selected from thegroup consisting of those compounds having the following formulas:

R5-O CH2) p-O-R6 and R5O (R7O qR7OR6 wherein p represents a positiveinteger of from 2 to 12 inclusive, R5 and R6 each represents asubstituent selected from the group consisting of a hydrogen atom and anacyl radical containing from 2 to 4 carbon atoms, R7 represents analkylene radical containing from 2 to 4 carbon atoms and q represents apositive integer of from 1 to 10 inclusive, the alpha, omega-dioxycompound being employed in such a proportion that there is at least anequivalent amount of alpha and omega oxy substituents in proportion tothe carbalkoxy substituents in the overall combination of the aromaticdiester and the alpha, omega-dioxy compound, (C) in the presence of acatalytic condensing agent which is an organo-tin compound selected fromthe group consisting of those compounds having the following formulas:

2( R)4 MH(Sn(OR) R)4) M' HS.. OR),),

M (Sn(OR)s) MH(Sn(OR)o) M'(Sn(OR)e) M'(HSTI(OR)5)2 Sn(OR)z Sn(OR)4 SnRzSl'lR'4 R'zSnO Sn R OAc wherein M represents an alkali metal, Mrepresents an alkaline earth metal selected from the group consisting ofmagnesium, calcium and strontium, R represents an alkyl radicalcontaining from 1 to 8 carbon atoms, R' represents a substituentselected from those consisting of an alkyl radical containing from 1 to8 carbon atoms and an aryl radical of the benzene series containing from6 to 9 carbon atoms, and Ac represents an acyl radical derived from anorganic acid containing from 2 to 18 carbon atoms, (D) at an elevatedtemperature which is increased gradually during the course of thecondensation up to a temperature of from about 225 to about 310 C., (E)the condensation being conducted in an inert atmosphere, (F) andconducting the condensation at a very low pressure of the inertatmosphere during the latter part of the condensation.

2. A process as defined in claim 1 wherein the condensing agent isemployed in an amount of from about 0.005% to about 0.2% based on theweight of the aromatic dicarboxylic acid diester.

3. A process as defined in claim 2 wherein the alpha, omega-dioxycompound is employed in such a proportion that there are from about 1.2to about 3 alpha and omega oxy substituents in proportion to thecarbalkoxy substituents in the overall combination of the aromaticdiester and the alpha, omega-dioxy compound.

4. A process as defined in claim 3 wherein the elevated temperatureemployed during the earlier part of the condensation is from about 150C. to about 220 C.

5. A process as defined in claim 4 wherein the low pressure definedunder (F) is less than 15 mm. of Hg pressure.

6. A process as defined in claim 5 wherein the low pressure definedunder (F) is less than 5 mm. of Hg pressure.

7. A process as defined in claim 6 wherein the aromatic diester isderived from p,p'-sulfonyl dibenzoic acid and the condensing agent isdibutyl tin diacetate.

8. A process as defined in claim 6 wherein the aromatic diester isderived from p,p'-sulfonyl dibenzoic acid and the condensing agent isdiphenyl dibutyl tin.

9. A process as defined in claim 6 wherein the aromatic diester isderived from p,p'-sulfonyl dibenzoic acid and the condensing agent isdibutyl tin oxide.

10. A process as defined in claim 6 wherein the aromatic diester isderived from p,p-sulfonyl dibenzoic acid and the condensing agent isdibutyl tin dichloride.

11. A process as defined in claim 6 wherein the aromatic diester isderived from terephthalic acid and the condensing agent is dibutyl tindibutoxide.

12. A process as defined in claim 1 wherein the aromatic dicarboxylicacid diester is formed by a preliminary step comprising condensing anaromatic dicarboxylic acid having the formula:

wherein R2, R3 and X are defined under (A), with an alpha, omega-dioxycompound which is defined under (B) and is employed in the proportionsset forth under (B), at an elevated temperature, after which preliminarystep the catalytic condensing agent which is defined under (C) is addedand the condensation is completed as defined under (D), (E) and (F).

13. A process as defined in claim 12 wherein the elevated temperatureemployed during the preliminary step is substantially that at whichreflux conditions subsist, and the condensing agent is employed in anamount of from about 0.005% to about 0.2% based on the weight of thearomatic dicarboxylic acid diester, the alpha, omega-dioxy compound isemployed in such a proportion that there are from about 1.2 to about 3alpha and omega oXy substituents in proportion to the acid substituentsin the overall combination of the aromatic diester and the alpha,omega-dioxy compound, the elevated temperature employed during theearlier part of the condensation to form the polyester is from about C.to about 220 C., the low pressure defined under (F) is less than about15 mm. of Hg pressure and all materials employed in the process aresubstantially anhydrous.

References Cited in the file of this patent UNITED STATES PATENTS2,257,384 Johnston Sept. 30, 1941 2,267,777 Yngve Dec. 30, 19412,307,092 Yngve Jan. 5, 1943 2,465,319 Whinfield et al Mar. 22, 19492,583,084 Burt Jan. 22, 1952 2,614,120 Caldwell Oct. 14, 1952

1. A PROCESS FOR PREPARING A POLYESTER COMPRISING (A) CONDENSING UNDERSUBSTANTIALLY ANHYDROUS CONDITIONS AN AROMATIC DICARBOXYLIC ACID DIESTERHAVING THE FORMULA: